1. Field of the Invention
The invention concerns a device for positioning at least one fixed point in a civil engineering structure and also relates to the use of such a device in the holding of such structures.
2. Description of Related Art
Civil engineering structures such as bridges or viaducts in particular comprise, first, supports which are connected to the ground and are considered fixed and, second, steel or concrete parts, such as bridge floors which rest on these supports and are subject to thermal expansion and, in the case of a concrete bridge floor, to contraction and creep.
In structures of this type, there are thus both fixed supports and one or a plurality of structure parts, such as one or a plurality of bridge floors, of which the length varies during the course of the year, such that the length of an 800 m bridge may vary by 400 mm for example. This continuous variation in length therefore gives rise to a relative movement between the bridge floor, which expands or contracts, and its supports, for example the pier heads which support the bridge floor.
In order to take account of these factors, the connection between the bridge floor and pier head is generally brought about by supports with sliding casings, having a low coefficient of friction, or by resilient supports and/or rigid mountings between the bridge floor and pier head, so as first to enable the bridge floor to expand and contract freely relative to the piers and supports supporting it and second to provide a fixed point somewhere on the bridge floor in order to prevent the latter's being able to move uncontrollably.
In order to comprehend the invention better, the essential means used according to the prior art will be described first with reference to FIGS. 1 to 6, whilst the invention will be described with reference to FIGS. 8 and 9, FIG. 7 explaining the result sought both by the prior art and the invention.
One of the fundamental problems posed is that of producing a fixed point which, in the case of a bridge floor for example, will ensure that said floor can expand and contract freely during the course of the year but will not move as a single unit and maintains a fixed anchorage point. If the fixed point is formed for example at a connection between one of the bridge piers and a corresponding point of the bridge floor and no particular precautions are taken, in the event of an earthquake, for example, since the pier cannot hold the bridge, the bridge will collapse under the effect of the movement caused by the pier. If, in order to avoid this problem occurring, the fixed support is designed such that, if stresses which are too great are applied, the fixed support is destroyed, for example as a result of the shearing of a retaining key, the problem will then be that the associated displacement movement of the bridge floor cannot be controlled and that, in the event of aftershocks, there will no longer be any fixed support at all to hold the bridge floor.